The present invention relates to a piston member comprising a piston rod provided with a piston reciprocating inside a cylinder barrel, said piston divides the cylinder barrel chamber into a proximal cylinder barrel chamber having a proximal capped end opposite the piston and a distal cylinder barrel chamber having a distal cylinder barrel end opposite the piston.
The invention further relates to an apparatus for continuous transporting apportioned batches of material to a recipient, such as a gasifier or reactor.
The invention further relates to methods of continuous transporting apportioned batches of material to a recipient, such as a gasifier or a reactor under high pressure.
In particular the present invention relates to the use of an apparatus and methods for transporting coal powder and other solid materials.
Gasification of fossil fuels, biomass or waste is currently widely used on industrial scales to generate electricity.
Gasification relies on chemical processes at elevated temperatures greater than 700° C., which puts a high demand on safety regulations when the raw material are continuously fed to the gasifier, in particular due to presence of toxic and explosive gases. In a gasifier, the carbonaceous raw material undergoes several different processes. First the pyrolysis process occurs as the carbonaceous particle heats up. Volatile gases are released and char is produced resulting in weight loss of coal. The process is dependent on the properties of the carbonaceous material and determines the structure and composition of the char, which will then undergo gasification reactions. Next the volatile products and some of the char reacts with oxygen to form carbon dioxide and carbon monoxide in a combustion process, which provides heat for the subsequent gasification reactions where the char reacts with carbon dioxide and steam to produce carbon monoxide and hydrogen. By introducing oxygen or air into a gasification system organic material is converted into carbon monoxide and energy, for driving a second reaction that converts further organic material to hydrogen and additional carbon dioxide.
The feeding of solids into a high pressure reactor has however always been difficult because of both high equipment costs and poor material characteristics. Lock hoppers, which are the most commonly used principle for feeding against a pressure, have serious problems in the very high consumption of inert gas used for pressurizing and transfer. This is especially the case for feeding solids with a low density or with a tendency to form bridges. One other major shortcoming of lock hoppers is that it is a batch type operation. Since the valves between hoppers must be operable with high concentration of solids while moved, the valves are subject to sticking and seal failure under the operating conditions. Both the depressurizing valve and the vent lines are subject to severe abrasive conditions as the result of the rapid movement of hard solids therethrough under the influence of the differential pressure. Such systems are thus subject to sequence control failures and unsuitable for continuous operation due to great costs.
EP 1 425 089 relates to a method and apparatus for transfer of particulate products between zones of different pressure. In a sluice system the particulate product is first transported through a portioning device, which produces a sequence of uniform product portions divided by uniform particle free spaces. Subsequently the product portions are transported individually through a sluice device, which comprises at least one sluice chamber and two pressure locks of which at least one at any time secures a pressure tight barrier between the two pressure zones, and the product portions are force loaded from the first zone into a sluice chamber by means of a piston screw, the axis of which is practically in line with the axis of the sluice chamber, and the product portions are force unloaded from the sluice chamber and into the second pressure zone by means of said piston screw or a piston or by means of gas, steam or liquid supplied at a pressure higher than that of the second pressure zone. The sealing surfaces of the apparatus described in EP 1 425 089 are very vulnerable to wear resulting in that the apparatus is prone to leak. If gas is used as the pressure fluid the gas that is compressed in the sluice chamber must be released as the sluice chamber has to be decompressed in order to be filled again. Thus the gas from the sluice chamber will be released to the atmosphere during each piston stroke. This means that either the apparatus can only feed into atmospheres that are not combustible, explosive or poisonous or the consumption of inert bleed gas, i.e. gas resulting from any leakage in the feeding mechanism, will be very high.